In the manufacture of translucent containers such as clear or colored glass bottles, various types of checks or other commercial variations can occur in the sidewalls of the containers. For example, variations known as split seams and vertical checks may be present in the sidewall of a container. These split seams and vertical checks are mirror-like reflective cracks that lie in a plane and extend generally radially from the longitudinal axis of the container. Many devices have been proposed for detecting such variations.
U.S. Pat. No. 4,584,469 discloses a device for detecting split seams and vertical checks in the sidewall of a glass container. A light source is positioned to one side of the container to direct light energy onto the container wall from a direction perpendicular and lateral to the container axis. The light source comprises an incandescent bulb and a cylindrical lens for projecting an image of the bulb filament onto the container sidewall in an elongated narrow tightly focused strip parallel to the container axis. A linear array camera is positioned to receive an image of the illuminated portion of the container from a direction perpendicular to the illumination and container axes. As the container is held in position and rotated about its axis, a radial planar check will eventually be rotated into a position to reflect light from the source to the detector. Thus, the vertical check or split seam is detected as a bright spot on what is otherwise a normally gray or dark background viewed by the detector. (Directional terms such as "vertical" assume vertical orientation of the container axis with the mouth opening upwardly, as is typical in the container inspection art.)
Although the device disclosed in the noted patent has enjoyed substantial commercial success, further improvements remain desirable. In particular, the device disclosed in the noted patent is limited in its ability to detect checks that are not precisely vertical and parallel to the container axis. That is, if a check is non-vertical, light incident on the check will be reflected by the check but not necessarily incident on the camera. It is therefore a general object of the present invention to provide an apparatus and method of the general character or type disclosed in the above-noted patent having enhanced ability to detect and inspect non-vertical radial checks (and split seams) in the container sidewall.